Refractory metal plates

ABSTRACT

A refractory metal plate is provided. The plate has a center, a thickness, an edge, a top surface and a bottom surface, and has a crystallographic texture (as characterized by through thickness gradient, banding severity; and variation across the plate, for each of the texture components 100//ND and 111//ND, which is substantially uniform throughout the plate.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority under 35 U.S.C. § 119(e) to provisionalapplication Ser. No. 60/963,616, filed Aug. 6, 2007, incorporated byreference herein in its entirety.

FIELD OF THE INVENTION

The present invention relates to plates of pure tantalum or otherrefractory metals with novel properties, and their utilization assputtering targets.

BACKGROUND OF THE INVENTION

The crystallographic texture of a plate used as a sputtering target isof great importance to the sputtering performance, particularly to theuniformity of thickness of the thin films deposited on substrates. Onlya plate with uniform texture throughout its volume will give optimumperformance, and users rely on a steady supply of plates with similartexture. However, the manufacture of plates by existing,state-of-the-art, methods does not produce uniform texture.

A tantalum plate produced from an electron-beam-melted ingot byconventional processing (1980's technology), i.e. side-forging, rollingand annealing, has a banded texture, a legacy of the large grains formedduring solidification. It also has a through-thickness texture gradient,caused by variation of the shear strain (through the thickness) inducedduring rolling. It may also show incomplete recrystallization, andgrain-size banding.

Various advances and improvements in processing tantalum ingots havebeen published:

Pokross, in ‘Controlling the Texture of Tantalum Plate’, JOM October1989, and Clark et al. in a series of 3 papers in MetallurgicalTransactions A in 1991 and 1992 described the value of bi-directionalrolling (also known as cross-rolling) and multiple anneals.

Michaluk et al., in U.S. Pat. Nos. 6,348,113 and 6,893,513, disclosesmethods of preparing tantalum plates that do not achieve high levels ofuniformity.

Jepson et al, in U.S. patent application Ser. No. 10/079,286, disclosesrefractory metal plates having a reduction in texture banding severityachieved by introducing upset/forge-back/anneal sequences.

Turner, in U.S. Pat. No. 6,331,233, discloses a process for preparingtantalum plates which reduces banding severity, but which results in arather strong through-thickness texture gradient.

Shah and Segal, in U.S. Pat. No. 6,348,139, disclose the use of alow-friction interfacial layer in upset forging to achieve a moreuniform strain. The use of low-friction interfacial layers in upsetforging of other materials has long been known (e.g., Morra and Jepson,Superalloys 718, 625, 706 Conference, 1997).

Field et al., “Microstructural Development in Asymmetric Processing ofTantalum Plate” in Journal of Electronic Materials, Vol 34, No 12, 2005,introduced the concept of asymmetric processing to achieve shear strainthroughout the thickness of a plate.

Kumar et al., in U.S. Pat. No. 6,521,173, disclose the manufacture ofmetal powder suitable for consolidation into plates for sputtering.Although powder consolidated by hot isostatic pressing has a random,perfectly uniform texture, some texture, including a through-thicknesstexture gradient, develops when the block of consolidated powder isrolled to plate and annealed.

Koenigsmann and Gilman, in U.S. Pat. Nos. 6,770,154 and 7,081,148,disclose tantalum sputtering targets made by powder-metallurgy withparticular proportions of various grain orientations and an absence ofvisible banding. Targets made in accordance with these patents butinvolving a rolling step would have a through-thickness texturegradient.

Advances have been made in measuring texture, and the measurements canbe used in such a way that the uniformity of texture can be describedquantitatively. The EBSD (electron back-scatter diffraction) techniquemeasures texture grain-by-grain (whereas X-ray diffraction, the onlytechnique available until the early 2000's, only measured an aggregateover the area irradiated, which covered many grains), and EBSD equipmentwhich can cover the full thickness of the plate in a reasonable time isnow available. Methods of quantifying texture uniformity were describedboth by Michaluk, in U.S. Pat. No. 6,348,113 and by Jepson in U.S.patent application Ser. No. 10/079,286, but both of these methods wererudimentary and unsatisfactory. Another method, somewhat improved, wasdescribed by Michaluk et al. in JOM, March 2002. Presently, an ASTMstandard for quantification of texture is being drafted, followinginitiatives of Sutliff and Jepson (unpublished), and the proposed ASTMstandard method will be used in the present application to describe theuniformity of texture.

Three factors must be calculated and used to give an overall view of thenon-uniformity of texture within a plate:

a) Through-thickness gradient

b) Banding severity

c) Variation across a plate.

If the same measurements of texture are made for a multiplicity ofplates made by the same process, the stability of the process from plateto plate can also be estimated.

The rate of sputtering from a grain in the target depends on theorientation of the crystal planes of that grain relative to the surface(ref. Zhang et al, “Effect of Grain Orientation on Tantalum MagnetronSputtering Yield”, J. Vac. Sci. Technol. A 24(4), July/August 2006).Also, certain crystallographic directions are preferred directions offlight of the sputtered atoms (ref. Wickersham et al, “Measurement ofAngular Emission Trajectories for Magnetron-Sputtered Tantalum”, Journalof Electronic Materials, Vol 34, No 12, 2005). The grains of asputtering target are so small (typically 50-100 μm diameter) that theorientation of any individual grain has no significant effect. However,the texture of an area of the sputtered surface (an area roughly 5 cm to10 cm diameter) can have a significant effect. Thus, if the texture ofone area on the surface of a target is different from the texture of anyother area, the thickness of the film produced is unlikely to be uniformover the whole substrate. Also, if the texture of a surface area isdifferent from that of the same area at some depth into the targetplate, the thickness of the film produced on a later substrate (afterthe target is used, or eroded, to that depth) is likely to be differentfrom that produced on the first substrate.

So long as the texture of one area, then, is similar to that of anyother, it is not important what that texture is. In other words, atarget plate in which every grain has a 111 orientation parallel to theplate normal direction (ND) is no better and no worse than one in whichevery grain has a 100 orientation parallel to ND, or than one whichconsists of a mix of 100, 111 and other grains, so long as theproportions of the mix remain constant from area to area.

Uniformity of film thickness is of major importance. In integratedcircuits, several hundred of which are created simultaneously on asilicon wafer, for example, too thin a film at one point will notprovide an adequate diffusion barrier, and too thick a film at anotherpoint will block a via or trench, or, if in an area from which it shouldbe removed in a later step, will not be removable. If the thickness ofthe film deposited is not within the range specified by the designer,the device will not be fit for service, and the total cost ofmanufacture up to the point of test is lost, since no repair or reworkis normally possible.

If the target does not have uniform texture, and thus does not provide apredictable, uniform sputtering rate, it is impossible, instate-of-the-art sputtering equipment, to control the variation ofthickness from one point on the substrate to another. Partial, but nottotal, control of variation of thickness from substrate to substrate,and from target to target, is possible using test-pieces. Use oftest-pieces, however, is time-consuming and costly.

With targets made according to the prior art, the non-uniformity oftexture found in the target plate caused unpredictability in thesputtering rate (defined as the average number of tantalum atomssputtered off the target per impinging argon ion), or a change in thesputtering rate as the target was used. Variations of sputtering ratecause variation of the thickness of the film produced from point topoint on the substrate, and also cause variation of average thickness ofthe film produced on the substrate from substrate to substrate, and fromtarget to target.

SUMMARY OF THE INVENTION

Accordingly, the present invention will considerably improve thepredictability, and the uniformity, of the thickness of the filmsproduced, and thus improve the ease of use of the targets.

The present invention allows production of plates where the texture issubstantially uniform throughout the volume of the plate. Also, thetexture of one plate manufactured in accordance with the invention issubstantially the same as that of any other plate manufactured by thesame method.

Starting with conventional EB-melted ingots, the process of the presentinvention uses improved forging techniques and improved rollingtechniques, such as those described in the U.S. patent applicationentitled “Methods of Controlling Texture of Plates and Sheets by TiltRolling” filed on even date herewith and incorporated by referenceherein, to introduce sufficient redundant work into the material toannihilate the texture of the ingot, then to introduce a controlledtexture. The particular sequence of forging, rolling and heat-treatingproduces a final microstructure with a uniformity of texture which hasnot been previously achieved.

Starting, alternatively, with metal powder, and using conventionalmethods of consolidating the powder, the process invented uses the sameimproved rolling techniques to produce a plate with improved uniformityof texture.

Accordingly, in one aspect the present invention provides a refractorymetal plate having a center, a thickness, an edge, a top surface and abottom surface, the refractory metal plate having a crystallographictexture (as characterized by through thickness gradient, bandingseverity; and variation across the plate, for each of the texturecomponents 100//ND and 111//ND) which is substantially uniformthroughout the plate.

In an additional aspect, the present invention provides a refractorymetal plate manufactured by ingot metallurgy having a center, athickness, an edge, a top surface and a bottom surface, the refractorymetal plate having a crystallographic texture as characterized bythrough thickness gradient; banding severity; and variation across theplate, for the texture components 100//ND and 111//ND, where the averagethrough-thickness gradient is less than or equal to 6% per mm, theaverage banding severity is less than or equal to 6%, and the averagevariation across the plate is less than or equal to 6%.

The present invention also provides a refractory metal platemanufactured by ingot metallurgy having a center, a thickness, an edge,a top surface and a bottom surface, the refractory metal plate having acrystallographic texture as characterized by through-thickness gradient;banding severity; and variation across the plate, for the texturecomponents 100//ND and 111//ND, where the maximum through-thicknessgradient is less than or equal to 13% per mm, the maximum bandingseverity is less than or equal to 8%, and the maximum variation acrossthe plate is less than or equal to 11%.

In yet another aspect, the present invention provides a refractory metalplate manufactured by ingot metallurgy having a center, a thickness, anedge, a top surface and a bottom surface, having a texture ascharacterized by through-thickness gradient for the texture components100//ND and 111//ND, where the average through-thickness gradient isless than or equal to 4% per mm.

Also provided is a refractory metal plate manufactured by ingotmetallurgy having a center, a thickness, an edge, a top surface and abottom surface, having a texture as characterized by through-thicknessgradient, where the average through-thickness gradient for the texturecomponent 111//ND is less than or equal to 2% per mm.

In an additional aspect, the invention provides a refractory metal platemanufactured by ingot metallurgy having a center, a thickness, an edge,a top surface and a bottom surface, having a texture as characterized bythrough-thickness gradient, where the maximum through-thickness gradientfor the texture components 100//ND and 111//ND is less than or equal to9% per mm.

In other aspects, the present invention provides a refractory metalplate manufactured by powder metallurgy having a center, a thickness, anedge, a top surface and a bottom surface, the refractory metal platehaving a crystallographic texture as characterized by through-thicknessgradient; banding severity; and variation across the plate, for thetexture components 100//ND and 111//ND, where the averagethrough-thickness gradient is less than or equal to 5% per mm, theaverage banding severity is less than or equal to 4%, and the averagevariation across the plate is less than or equal to 4%.

The present invention also provides a refractory metal platemanufactured by powder metallurgy having a center, a thickness, an edge,a top surface and a bottom surface, having a texture as characterized bythrough-thickness gradient, where the maximum through-thickness gradientfor the texture components 100//ND and 111//ND is less than or equal to3% per mm.

The present invention further relates to methods, such as a method ofmaking a refractory metal plate, the method comprising the steps of:

-   -   i) providing an EB-melted ingot;    -   ii) cleaning the surface of the ingot;    -   iii) cutting the ingot into lengths to provide workpieces;    -   iv) processing each workpiece with at least three cycles of        upset-forge and forge-back;    -   v) annealing each workpiece at least three times, before or        after an upset-forge/forge-back cycle, providing adequate strain        for at least partial recrystallization in each cycle;    -   vi) cutting each workpiece into a size suitable for a target        plate;    -   vii) rolling each plate asymmetrically to the desired thickness;        and    -   viii) annealing after rolling, to achieve substantially full        recrystallization.

In an additional aspect, the invention includes a method of rolling ametal plate, the method comprising the step of applying shear to themid-thickness of the metal plate by means of tilted entry into the roll.

A further aspect of the invention includes a method of making arefractory metal plate, the method comprising the steps of:

-   -   i) providing a billet prepared by powder metallurgy methods;    -   ii) annealing the billet;    -   iii) cutting each billet into a size suitable for a target        plate;    -   iv) rolling each plate asymmetrically to the desired thickness;        and    -   v) annealing after rolling, to achieve substantially full        recrystallization.

The present invention also provides a refractory metal platemanufactured by ingot metallurgy having a center, a thickness, an edge,a top surface and a bottom surface, having a texture as characterized bythrough-thickness gradient for the texture components 100//ND and111//ND, where the average through-thickness gradient is less than orequal to 4% per mm, and the texture of which is substantially the sameas any other plate made by the same method.

And, the present invention provides a refractory metal platemanufactured by powder metallurgy having a center, a thickness, an edge,a top surface and a bottom surface, having a texture as characterized bythrough-thickness gradient, where the average through-thickness gradientfor the texture components 100//ND and 111//ND is less than or equal to2% per mm, and the texture of which is substantially the same as anyother plate made by the same method

These and other aspects of the present invention will become morereadily apparent from the following drawings, detailed description andappended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The file of this patent contains at least one color photograph. Copiesof this patent with color photographs will be provided by the Patent andTrademark Office upon request and payment of the necessary fee.

The invention is further illustrated by the following drawings in which:

FIGS. 1A, 1B and 1C are grain maps of tantalum plates in accordance withExample 1;

FIG. 1D is a graph of the results of measurements of the plate ofExample 1;

FIGS. 2A, 2B and 2C are grain maps of a tantalum plate in accordancewith Example 2;

FIG. 2D is a graph of the results of measurements of the plate ofExample 2;

FIGS. 3A, 3B, 3C and 3D are grain maps of a tantalum plate in accordancewith Example 3;

FIG. 3E is a graph of the results of measurements of the plate ofExample 3;

FIGS. 4A and 4B are grain maps of a tantalum plate in accordance withExample 4;

FIG. 4C is a graph of the results of measurements of the plate ofExample 4;

FIGS. 5A, 5B and 5C are grain maps of a tantalum plate in accordancewith Example 5;

FIG. 5D is a graph of the results of measurements of the plate ofExample 5;

FIGS. 6A, 6B and 6C are grain maps of a tantalum plate in accordancewith Example 6; and

FIG. 6D is a graph of the results of measurements of the plate ofExample 6.

FIGS. 7A, 7B and 7C are grain maps of a tantalum plate in accordancewith Example 7; and

FIG. 7D is a graph of the results of measurements of the plate ofExample 7.

FIGS. 8A, 8B, 8C and 8D are grain maps of a tantalum plate in accordancewith Example 8; and

FIG. 8E is a graph of the results of measurements of the plate ofExample 8.

DETAILED DESCRIPTION OF THE INVENTION

As used herein in the specification and claims, including as used in theexamples and unless otherwise expressly specified, all numbers may beread as if prefaced by the word “about”, even if the term does notexpressly appear. Also, any numerical range recited herein is intendedto include all sub-ranges subsumed therein. All ranges include theendpoints cited.

A—Ingot Metallurgy

A conventional EB (electron beam)—melted ingot is used as the startingpoint. It may be of any purity commonly used for sputtering targets(typically, “3 nines 5” to “5 nines 5”). Preferably, the ingot is atleast 99.95% pure, more preferably at least 99.995% pure. Purity, asused herein, refers to elimination of metallic impurities, notinterstitial impurities. A conventional EB-melted ingot consists of anear-surface region of grains nucleated at the surface (approximatelyequiaxed, with about 1 cm size) and a central region of long grains,with the long axis parallel to the ingot axis. The crystallographicorientation of the grains is not controlled in any way.

In one embodiment, the present invention provides a method of making arefractory metal plate having a center, a thickness, an edge, a topsurface and a bottom surface, the method comprising the steps of:

-   -   i) providing an EB-melted ingot;    -   ii) cleaning the surface of the ingot;    -   iii) cutting the ingot into lengths to provide workpieces;    -   iv) processing each workpiece with at least three cycles of        upset-forge and forge-back;    -   v) annealing each workpiece at least three times, before or        after an upset-forge/forge-back cycle, to provide adequate        strain for at least partial recrystallization with each cycle;    -   vi) cutting each workpiece into a size suitable for a target        plate;    -   vii) rolling each plate asymmetrically to the desired thickness;        and    -   viii) annealing after rolling, to achieve substantially full        recrystallization.

Substantially full “recrystallization”, as used herein, is a term ofart, known to those skilled in the art of metallurgy, and refers to aplate having at least 85%, 90%, 95%, 96%, 97%, 98%, 99%, 99.5%, orhigher recrystallization. Typically, the amount of recrystallization isdetermined after the final annealing step, when a sample is taken fromthe edge of the plate and examined microscopically.

In one embodiment, the refractory metal plate is further processed withone or more processing steps selected from the group consisting ofcleaning the surface before each annealing, upset forge to cheese,flattening, and cutting to size after rolling.

For example, the ingot can be processed in accordance with oneembodiment of the method for ingot-processing as described in U.S.patent application Ser. No. 10/079,286 (para 29), incorporated herein byreference. Specifically, the operations are:

-   -   1) Clean the surface of the ingot by machining.    -   2) Cut the ingot into lengths    -   3) Upset forge (U1)    -   4) Anneal (A1)    -   5) Forge-back to approximately the original dimensions (FB1)    -   6) Upset forge (U2)    -   7) Forge-back to approximately the original dimensions (FB2)    -   8) Anneal (A2)

Subsequently, the operations diverge from the cited embodiment of U.S.Ser. No. 10/079,286. An example of a sequence of operations in anembodiment of the present invention is the following:

-   -   9) Upset forge (U3)    -   10) Forge-back to a diameter less than the original diameter        (FB3)    -   11) Anneal (A3)    -   12) Forge-back further (FB4)    -   13) Clean the surface by machining    -   14) Cut the billet into lengths, each piece being of the        required weight to make one target plate    -   15) Upset forge to cheese (UC)    -   16) Roll to the desired thickness.    -   17) Anneal (A4)    -   18) Flatten    -   19) Cut to size.

In general, the anneals can be placed wherever desired; it is notrequired to have an anneal following each upset/forge-back sequence. Thepositions of the anneals are arranged so that (a) there is enough strainput in throughout the volume to cause substantially completerecrystallization during the anneal, but (b) there is not so much strainthat either the material becomes so strong that the forging press runsout of strength or the workpiece begins to crack. Preferably, annealingis done as soon as possible after the true strain in the least-strainedpart of the volume reaches a value of 1. However, the first anneal ispreferably done at lower strain because the workpiece at this stage ismore susceptible to cracking.

Operations 9, 10, 11, 12 and 13 are performed in the same manner assimilar operations described in U.S. application Ser. No. 10/079,286.

Operations 2 through 11 constitute three “strain-and-anneal” cycles. Thedimensions of the individual work-pieces before and after each operationare arranged such that the strain in every element of the volume of theworkpiece in each cycle is at least about 1, as a rule of thumb, andsuch that that strain is composed of comparable strain components in the3 orthogonal “principal-strain” directions.

Operation 12 is optional. It is used for small sputtering-target plates(for example, those used to sputter 200 mm silicon wafers), but not forlarge plates (for example, those used to sputter 300 mm silicon wafers).

Operation 14 is carried out on a band-saw or any similar suitablecutting equipment.

Operation 15 is carried out with a low-friction layer between top dieand workpiece, and between bottom die and workpiece. A plate of aluminum(such as Al alloy 1100, in a soft temper), ¼″ thick, has been found tobe suitable; other metals and metal alloys can also be used. Operation15 is optional. It is used for thick sputtering-target plates (thosegreater than about 0.300″ thickness), but not for thinner ones.

Operation 16 is done on a conventional rolling mill (for example, ahorizontal reversing 4-high single-stand mill with 16″ diameter rolls),but under special conditions, such as those described in the U.S. patentapplication entitled “Methods of Controlling Texture of Plates andSheets by Tilt Rolling” filed on even date herewith, incorporated byreference herein, also described in more detail below.

Operations 17, 18 and 19 may be done in any order. They are all carriedout in a conventional manner.

After Operation 19, the plate is bonded to a backing plate, machined tofinish, and cleaned, to form a finished planar sputtering target. Anyaccepted method may be used for these operations. The sputtering targetis subsequently sputtered, for example with a DC magnetron sputteringprocess, to form a thin film of tantalum on a substrate such as asilicon wafer. Although the advantages of this invention will be lessnoticeable with older generations of sputtering equipment, becausenon-uniformity due to target variation might be small compared tonon-uniformity due to other causes, modern sputtering equipment,particularly that designed to produce integrated circuits with a 65 nmor smaller design rule, will especially benefit from this invention.

B—Powder Metallurgy

The powder is manufactured and processed in accordance with the methoddescribed in U.S. Pat. No. 6,521,173, forming a cylindrical billet.

Specifically, the operations are:

1) Cold Isostatically Press (CIP) the powder to 60-90% density;

2) Encapsulate the pressed preform in a steel can and evacuate and sealthe can;

3) Hot Isostatically Press (HIP) the preform to a billet with 100%density;

4) Remove the steel can;

5) Anneal the billet; and

6) Cut, using a band-saw or any similar suitable cutting equipment, intoslices suitable for rolling into a plate: the slices have the shape of ahockey puck.

The puck is rolled exactly in accordance with the rolling describedabove for Ingot-Metallurgy (Operation 16).

After rolling, the plate is processed and treated exactly as describedabove for Ingot-Metallurgy (Operations 17, 18 and 19, bonding to abacking plate, etc.).

Refractory metal plates made by the above methods, where ingot derived,will have an average through-thickness gradient of less than or equal to6% per mm, more preferably less than 4%, most preferably less than 3%,for the texture components 100//ND and 111//ND.

The maximum through-thickness gradient of ingot derived plates will beless than or equal to 13% per mm, more preferably less than 9%, mostpreferably less than 8% for the texture components 100//ND and 111//ND.

Ingot derived plates will have an average banding severity of less thanor equal to 6%, and the maximum banding severity is less than or equalto 8%, for the texture components 100//ND and 111//ND.

Ingot derived plates will have an average variation across the plate ofless than or equal to 6%, more preferably less than or equal to 5%, forthe texture components 100//ND and 111//ND.

The maximum variation across the plate for ingot derived plates is lessthan or equal to 11%, more preferably less than 7%, for the texturecomponents 100//ND and 111//ND.

In one embodiment, ingot derived refractory metal plates of theinvention will have an average through-thickness gradient for thetexture component 111//ND less than or equal to 2% per mm.

Refractory metal plates made by the above methods, where made by powdermetallurgy methods (powder met), will have an average through-thicknessgradient of less than or equal to 5% per mm, more preferably less than2%, for the texture components 100//ND and 111//ND.

The maximum through-thickness gradient of powder met plates is less thanor equal to 8% per mm, more preferably less than 3%, for the texturecomponents 100//ND and 111//ND.

Powder met plates will have an average banding severity of less than orequal to 5%, more preferably less than 4%, for the texture components100//ND and 111//ND.

The maximum banding severity of powder met plates is less than or equalto 7%, more preferably less than or equal to 5%, for the texturecomponents 100//ND and 111//ND.

Powder met plates will have an average variation across a plate lessthan or equal to 4%, and a maximum variation across a plate of less thanor equal to 7%, for the texture components 100//ND and 111//ND.

For measurements of through-thickness gradient, such as average andmaximum gradient, and variations across the plate or from plate toplate, the lower bound is 0%, i.e., it may in some cases be possible toachieve zero variation or gradient. For measurements of banding, thelower bound is about 2%; levels lower than this are difficult to achieveor detect due to the noise in measurement of this property.

Some advantages of the methods of the present invention may be achievedby 1) the use of at least three cycles of upset-and-forge-back to breakup the ingot grain structure and homogenize the texture, 2) the use ofaluminum or other metal plates to improve (make more homogeneous) thestrain distribution in cheese upset, 3) the use of an inclined plane tofeed the workpiece into the rolling mill, and 4) control of rolling sothat the curl is controlled, and similar from pass to pass and fromworkpiece to workpiece. Although control of curl for the purpose ofeasing subsequent operations is practiced routinely, control of curl forthe purpose of minimizing variation of texture from workpiece toworkpiece is novel.

The use of an inclined plane is referred herein as “tilt rolling” or“tilted entry”. It makes the rolling process asymmetric as compared tostandard rolling processes, which are symmetric, in that there is aplane of symmetry corresponding to the mid-thickness plane of theworkpiece. Asymmetric rolling is sometimes used, for example, whenrolling aluminum sheet, to improve the result of a subsequentdeep-drawing operation (for example, “Development of Grain Structure andTexture during Annealing in Asymmetrically-Rolled AA5754”, H. Jin and D.J. Lloyd, Materials Science Forum Vols 467-470 (2004), p. 381).Asymmetric rolling to improve the sputtering performance of a tantalumplate was introduced by Field et al. in 2005 (as referenced inBackground), but asymmetry was introduced in one of the following ways:

1) Use of rolls (top and bottom work rolls) rotating at different speeds

2) Use of rolls (top and bottom work rolls) of different diameters

3) Use of rolls (top and bottom work rolls) with different frictioncoefficients.

Accordingly, in the methods of the present invention, the term“asymmetric rolling” will refer to tilted entry or tilt rolling. Rollingwill be carried out according to the present invention using an angle ofincline of between 2% and 20%, more preferably an angle of incline of atbetween 3 and 7%. As would be understood by one skilled in the art,typically the angle will be above horizontal, i.e. the sheet or plate isfed downward into the roll. In some cases, however, such as inmulti-stand rolling, the angle may be below horizontal, and the plate orsheet is fed upward into the roll. As used herein, the term “angle ofincline” refers to both modes of feeding the plate/sheet into the roll.

Compared to all other tantalum plates currently available, and comparedto all other claims of texture uniformity of ingot-derived tantalumplate published as papers or patent documents, the product made by theprocess of the present invention has more uniform texture, substantiallycompletely uniform, as measured in accordance with the draft ASTMStandard Method, and reported as Through-Thickness Gradient, BandingSeverity, Variation Across a Plate, and Variation from Plate to Plate.Substantially uniform texture means, in this context, only slightvariations in texture, at the limits of detection using the bestavailable methods, for example, a through-thickness gradient of nogreater than 3% per mm, a banding severity no greater than 5%, and avariation across the plate no greater than 6%, due to the imperfectprecision of measurement.

In particular, the Through-Thickness Gradient is reduced, compared tothe prior art, while Banding Severity and Variation Across a Plate andVariation from Plate to Plate are at least as good as the prior art.

“Substantially the same”, in the context of variation from plate toplate, means that if the texture of each of a large number of plates isquantified by the 6 parameters shown in Table 10 (below), and thestandard deviation of the population of each parameter is less than 4,all the plates in that population are said to have substantially thesame texture.

The grain size of the plates is not compromised by the specialprocessing needed to obtain uniform texture. An average grain size(linear intercept) of less than 80 μm is normally achieved, and in someembodiments is less than 60 μm.

In some embodiments, during rolling the workpiece is rotated apre-determined angle about a vertical axis between passes. In thiscontext, “pre-determined” means that an angle is chosen and used forevery rotation.

In some embodiments, the thickness reduction per pass is pre-determined.In other embodiments, the workpiece is turned over at regular intervals.In yet additional embodiments, a lubricant is applied to the top andbottom surfaces of the workpiece and the rolls are maintained at aconstant roughness.

Variation from plate to plate can be minimized by using the sameparameters for rotation, thickness reduction, turning over, lubricationand roughness.

Powder-metallurgy processing has the advantage (over ingot-metallurgyprocessing) of producing, in general, more uniform texture. However, ithas certain disadvantages, including higher impurity content.Powder-metallurgy plates made according to the present invention have alower through-thickness texture gradient than any previouspowder-metallurgy plate.

The sputtering performance of targets made from this plate will be morepredictable, and more consistent as a target is used (i.e. frombeginning of life to end of life), and more consistent from target totarget, than targets made according to the prior art.

EXAMPLES

The invention is further illustrated by the following examples, whichare not meant to be limiting.

Example 1 (Comparative)

A plate was produced in accordance with U.S. patent application Ser. No.10/079,286, paragraphs 26, 28 and 29. A total of 3 annealings (2intermediate, 1 final) were carried out.

Samples were taken from the centre of the plate, the mid-radius of theplate and the edge of the plate, and the texture determined by EBSD,using a 15 μm step in both horizontal and vertical directions. The platewas 6 mm thick. The average grain size was about ASTM 6 (40 micronsAverage Linear Intercept (ALI) distance). The results are presented herein various ways.

First, grain maps of the full thickness of samples from the threelocations are shown in FIGS. 1A, 1B and 1C. The top edge of the map isone rolled surface, and the bottom edge is the other rolled surface.Note that the plate, as-rolled, was slightly thicker in the centre thanat the edge. The width examined (the horizontal length of each map) is1.5 mm. The maps show the grains which have particular crystallographicdirections within 15° of the plate Normal Direction (the verticaldirection on the maps). Grains with 100 within 15° of ND (known as the100//ND component) are red, those with 111 within 15° of ND (the 111//NDcomponent) are blue, and those with 110 within 15° of ND are yellow.Grains which satisfy none of the criteria are grey. The percentages ofarea occupied by these color blocks form the basis of calculation of thenumerical factors addressed below.

Second, the maps are analyzed mathematically as follows:

1) The maps are divided into two halves, the top half (H1) and bottomhalf (H2).

2) A mask, with a cut-out hole 135 μm high, but full-width (1.5 mm inthis case), is placed over the map, such that the top of the cut-outhole corresponds to the top of the map. Note that the height of thewindow (in this case 135 μm) is chosen to be approximately 3 grains, butan integral number of EBSD steps (in this case, 9 steps).

3) The percentage of the area of the cut-out hole occupied by red coloris calculated, as is the percentage occupied by blue color.

4) The mask is moved down by one step (in this case 15 μm), and thecalculations repeated.

5) Operation 4 is repeated until the bottom of the cut-out holecorresponds to the bottom of the map.

6) A graph (FIG. 1D) is made showing the results. For example, thisgraph is for the top half of the centre sample. The Y axis shows thearea percentage, from 0% to 70%, while the X axis shows the position ofthe mask cut-out, from the top of the map (left side) to mid-thickness(right side). The red dots refer to 100, while the blue dots refer to111.

7) This data is analyzed to determine, for each half of the thickness:

-   -   a) The gradient of the best-fit straight line through the 100        data, expressed as % per mm (100 Grad).    -   b) The gradient of the best-fit straight line through the 111        data, expressed as % per mm (111 Grad).    -   c) The average distance (in the y-direction) of each 100        data-point from the best-fit straight line, (which, if it would        go below zero, is counted as zero), expressed as % (100 BF)    -   d) The average distance (in the y-direction) of each 111        data-point from the best-fit straight line (which, if it would        go below zero, is counted as zero), expressed as % (111 BF).

The results of this analysis, for both half-thicknesses of the threespecimens, are:

TABLE 1A 100Grad 111Grad 100BF 111BF Centre H1 −4.06 4.93 8.40 6.63Centre H2 0.70 2.04 6.86 9.10 Mid-Rad H1 −9.55 14.45 5.05 4.95 Mid-RadH2 4.80 −0.61 6.55 8.54 Edge H1 −8.33 13.94 6.66 7.61 Edge H2 6.22 −7.749.23 7.47

8) Finally, the variation across a plate is calculated. This calculationis not included in the draft ASTM Standard Method. It is best evaluatedfrom the following table, which shows the area percentage of 100 and 111within 15° of ND for each half-thickness of each sample. The range isthe difference between greatest and smallest numbers in the row. Notethat the mask with a cut-out is not used in this calculation.

TABLE 1B Centre Mid-Rad Edge A/P Range H1-100 38 39 28 11 H1-111 22 2730  8 H2-100 39 34 27 12 H2-111 22 35 44 22

-   -   ‘100 Grad’ and ‘111 Grad’ are measures of the through-thickness        gradient.    -   ‘100BF’ and ‘111BF’ are measures of the banding severity.    -   ‘A/P Range’ is a measure of the variation of the texture across        a plate.

Example 2 (Comparative)

A plate was produced in accordance with U.S. Pat. No. 6,331,233,‘Detailed Description’ and FIG. 3. The average grain size was about ASTM5 (60 microns ALI).

Samples were taken from the centre of the plate, the mid-radius of theplate and the edge of the plate, and the texture determined by EBSD,using a 15 μm step in both horizontal and vertical directions. The platewas 9 mm thick, and the width examined was 3.6 mm. A window height of180 μm was used. The results are presented in the same manner as Example1 (except the graph shows area percentage from 0% to 90% rather than 0%to 70%) in FIGS. 2A, 2B, 2C and 2D, and in Tables 2A and 2B.

TABLE 2A 100 Grad 111 Grad 100BF 111BF Centre H1 −4.40 12.47 7.38 7.93Centre H2 2.26 −10.18 6.78 6.39 Mid-Rad H1 −7.11 13.29 5.25 5.83 Mid-RadH2 9.69 −12.00 4.85 6.78 Edge H1 −8.24 6.39 4.86 4.77 Edge H2 6.65 −5.235.00 5.12

TABLE 2B Centre Mid-Rad Edge A/P Range H1-100 20.9 19.3 27.4 8.1 H1-11126.5 27.0 22.1 4.9 H2-100 16.2 21.4 22.8 6.6 H2-111 25.5 28.0 21.9 6.1

Example 3 (Comparative)

Three plates 7 to 8 mm thick were produced by a powder-metallurgyprocess in accordance with U.S. Pat. No. 6,521,173 and the process givenabove (steps 1 to 6), resulting in pucks 165 mm diameter and 81 mmthick. The pucks were rolled using conventional techniques (including anannealing step at 33 mm thickness), and finish-processed conventionally.

Samples were taken from the centre of each plate, the mid-radius of eachplate and the edge of each plate (2 samples, well separated), and thetexture determined by EBSD, using a 10 μm step in both horizontal andvertical directions. The results are presented in Tables 3 A and 3B inthe same way as for Example 1, except that the width examined was 1.64mm rather than 1.5 mm, and the graph shows area percentage from 0% to60% rather than 0% to 70%. Grain maps of Plate 1 are presented in FIGS.3A, 3B, 3C and 3D, with results of Centre—H1 displayed in FIG. 3E. Theaverage grain size was about ASTM 7 (28 microns ALI).

TABLE 3A Plate 1 100 Grad 111 Grad 100 BF 111 BF Centre H1 −4.09 1.714.58 5.56 Centre H2 1.93 −3.10 5.44 5.56 Mid-Rad H1 −5.95 4.0 4.61 4.40Mid-Rad H2 4.28 3.89 5.22 4.63 Edge 1 H1 −3.28 6.32 4.39 4.84 Edge 1 H25.19 −2.48 4.50 5.32 Edge 2 H1 −5.64 4.70 3.63 4.68 Edge 2 H2 7.94 −4.474.34 5.45 Plate 2 Centre H1 −6.34 4.96 5.96 5.44 Centre H2 4.55 −6.925.24 5.48 Mid-Rad H1 −6.48 7.97 5.79 5.51 Mid-Rad H2 5.54 −9.04 3.735.29 Edge 1 H1 −6.50 8.00 5.13 5.99 Edge 1 H2 6.36 −7.48 4.90 6.57 Edge2 H1 −7.57 8.48 5.09 7.32 Edge 2 H2 −7.61 8.79 4.04 7.06 Plate 3 CentreH1 −5.20 4.97 4.65 7.08 Centre H2 4.38 −2.14 4.29 6.74 Mid-Rad H1 −8.365.76 5.58 6.67 Mid-Rad H2 5.96 −6.74 4.77 7.86 Edge 1 H1 −4.93 5.60 3.575.35 Edge 1 H2 4.89 −4.46 4.53 5.16 Edge 2 H1 −5.07 3.91 4.11 6.05 Edge2 H2 7.80 −7.46 4.91 4.84

TABLE 3B Plate 1 Centre Mid-Rad Edge 1 Edge 2 A/P Range H1-100 23.7 27.823.2 22.7 5.1 H1-111 25.2 22.3 28.2 29.9 7.6 H2-100 27.1 26.3 27.3 26.01.3 H2-111 21.5 25.4 29.2 29.8 8.3 Plate 2 H1-100 26.5 26.9 26.8 22.93.9 H1-111 28.5 30.2 29.8 31.8 3.3 H2-100 23.8 20.9 23.5 21.7 2.9 H2-11129.0 30.2 33.1 27.3 5.8 Plate 3 H1-100 23.4 24.8 23.2 21.4 3.4 H1-11130.5 35.1 31.4 34.4 4.6 H2-100 27.1 22.0 27.0 26.0 5.1 H2-111 31.7 35.229.9 30.9 5.3

Example 4 (Comparative)

Nineteen plates were produced in accordance with U.S. patent applicationSer. No. 10/079,286, paragraphs 26, 28 and 29, but differing fromExample 1 in that a total of 4 annealings (3 intermediate, 1 final) werecarried out. The plates were about 10 mm thick.

One sample was taken from the edge of each plate. The texture of eachsample was determined by EBSD, using a 15 μm step in both horizontal andvertical directions. The results are presented in FIGS. 4A, 4B and 4C,and in Table 4A, in the same way as Example 1, except that because onlyedge samples were taken, no A/P range can be calculated. The averagegrain size was about ASTM 5 (53 μm ALI).

TABLE 4A 100 Grad 111 Grad 100 BF 111 BF  1-H1 −8.17 9.66 7.01 7.68 1-H2 4.28 −8.70 5.16 7.63  2-H1 −3.22 2.93 7.47 8.43  2-H2 1.76 −6.995.33 9.09  3-H1 −4.48 11.24 2.96 7.40  4-H2 6.06 −7.92 4.04 8.88  4-H1−5.23 3.43 4.46 5.87  4-H2 6.88 −9.12 5.87 6.63  5-H1 −7.35 8.89 4.467.33  5-H2 8.22 −10.00 4.68 8.94  6-H1 −5.69 9.73 3.38 7.96  6-H2 4.89−8.88 3.28 4.55  7-H1 −5.90 4.07 3.67 4.17  7-H2 4.91 −4.29 3.83 7.37 8-H1 −4.38 4.28 5.39 4.69  8-H2 6.81 −9.14 4.58 6.81  9-H1 −4.42 8.243.78 5.98  9-H2 8.55 −11.81 5.60 5.79 10-H1 −4.15 9.15 7.33 8.11 10-H25.12 −6.89 7.37 10.58 11-H1 −4.96 9.04 6.80 8.35 11-H2 4.00 −7.20 4.276.93 12-H1 −6.71 10.51 3.53 12.23 12-H2 5.41 −15.09 3.11 9.98 13-H1−4.10 7.45 4.28 6.80 13-H2 7.15 −6.80 7.39 6.04 14-H1 −4.23 8.69 4.257.11 14-H2 4.15 −6.75 5.52 6.64 15-H1 −9.43 13.33 4.70 8.10 15-H2 4.51−8.42 6.72 9.68 16-H1 −5.34 9.23 5.33 8.58 16-H2 4.19 −8.71 3.30 6.4317-H1 −4.20 5.39 4.54 8.16 17-H2 5.97 −10.32 4.63 7.23 18-H1 −4.73 11.562.39 7.43 18-H2 3.46 −11.78 3.52 4.43 19-H1 −5.38 11.46 2.95 11.00 19-H25.48 −13.41 3.76 5.18

Example 5 (Inventive)

A plate 6 mm thick was made, using the ingot-metallurgy process outlinedabove, including the following process details:

1) Clean the surface of the ingot by machining. Cut the ingot (195 mmdiameter) to length, 374 mm, resulting in a weight of 474 lbs.

2) Upset forge (U1) the billet to 65% of initial billet length

3) Anneal (A1) billet at 1370 C

4) Forge-back billet to 197 mm diameter (FB1)

5) Upset forge (U2) billet to 65% of initial billet length

6) Forge-back billet to 197 mm diameter (FB2)

7) Upset forge (U3) billet to 65% of initial billet length

8) Anneal (A2) billet at 1065 C

9) Forge-back the billet to 133 mm diameter (FB3). Clean the surface bymachining, thus reducing the billet diameter to 127 mm

10) Cut the billet to length, 38.1 mm

11) Anneal (A3) billet at 1065 C

12) Roll to thickness. A 10-degree tilt angle was used. The thickness ofthe piece was reduced by approximately 5% in each pass. The piece wasrotated 90 degrees about a vertical axis after each pass. The piece wasturned over after every 4 passes. The final thickness of the piece afterrolling was 6 mm.

13) Anneal (A4) at 1065 C

14) Flatten

15) Samples were taken from the centre of the plate, the mid-radius ofthe plate and the edge of the plate, and the texture determined by EBSD,using a 15 μm step in both horizontal and vertical directions. Theresults are presented here in the same way as for the Example 1, exceptthat the width examined was 1.64 mm rather than 1.5 mm, and the graphshows area percentage from 0% to 60% rather than 0% to 70%. Grain mapsand graphical results are shown in FIGS. 5A, 5B, 5C and 5D,respectively. The average grain size was about ASTM 6 (approximately 40μm ALI).

TABLE 5A 100 Grad 111 Grad 100 BF 111 BF Centre H1 −2.00 −0.21 6.14 5.84Centre H2 −2.24 −2.59 5.86 3.52 Mid-Rad H1 −1.83 −0.41 6.69 7.77 Mid-RadH2 2.51 −8.49 5.60 5.20 Edge H1 −3.29 3.98 7.78 4.59 Edge H2 3.08 −3.695.43 7.63

TABLE 5B Centre Mid-Rad Edge A/P Range H1-100 27 28 32 5 H1-111 26 26 282 H2-100 30 35 37 7 H2-111 22 22 23 1

Use of Other Measurement Procedures

The Centre sample of the plate made in Example 5 (as an example of theinvention) is analyzed in the manners previously used and mentionedabove.

Using the method described in U.S. Pat. No. 6,348,113, viz.:

The thickness was divided into 20 increments. For each increment, thepeak intensity was calculated using a 10° half-width (which is notspecified in '113, but is standard in the industry).

TABLE 5C Increment 111 100 In (ratio)  1 3.95 7.43 −0.63  2 5.07 450 0.12  3 3.55 3.58 −0.01  4 2.07 3.98 −0.65  5 2.25 2.35 −0.04  6 2.263.29 −0.38  7 2.94 3.12 −0.06  8 2.59 3.27 −0.23  9 2.43 5.29 −0.78 104.53 4.71 −0.04 11 4.10 6.22 −0.42 12 2.54 6.34 −0.91 13 2.45 4.75 −0.6614 3.24 3.65 −0.12 15 2.65 4.70 −0.57 16 1.83 3.25 −0.57 17 2.40 3.71−0.44 18 1.55 4.63 −1.09 19 3.20 5.38 −0.52 20 3.55 6.18 −0.55

The 111 peak intensity varies from 1.55 to 5.07, whereas the 111 peakintensity in Plate 125B (one of the best examples in '113) varies from0.85 to 6.06. The 100 peak intensity varies from 2.35 to 7.43, whereasthe 100 peak intensity in Plate 125B varies from 0.27 to 10.65. The In(111/100) varies from −1.09 to 0.12, whereas the In (111/100) in Plate125B varies from −2.53 to 3.11.

Thus, by the method of quantifying texture described in '113, theinventive example is much more uniform through the thickness than eventhe best example in '113. However, this method is not a good method ofcomparison, compared to the ASTM draft method used above.

Using the method described in U.S. patent application Ser. No.10/079,286, viz:

The thickness was divided into 8 increments. The number of increments isnot specified in '286, but 8 is typical, and the number of increments isnot critical. For each increment, the % of the area within 15° of 100,and within 15° of 111, is calculated, and the difference (thedistribution) is further calculated.

TABLE 5D Increment # 100-15 111-15 Difference 1 34 31  3 2 23 20  3 3 2223  1 4 29 32  3 5 36 28  8 6 29 22  7 7 23 18  5 8 32 22 10

The minimum difference is 1% and the maximum difference is 10%,resulting in a distribution of 9%. Thus it can be seen that thedistribution of texture of the inventive example, 9%, is much less thanthe distribution achieved previously, as U.S. patent application Ser.No. 10/079,286 claimed a distribution of less than 30%, and plates madeaccording to that process typically achieved a distribution of 25%.However, this method of comparison is not a good method, compared to theASTM draft method used above.

Example 6 (Inventive)

A plate 7.5 mm thick was made, using the ingot-metallurgy processoutlined above, including the following process details:

1) Clean the surface of the ingot by machining. Cut the ingot (195 mmdiameter) to length, 374 mm, resulting in a weight of 474 lbs.

2) Upset forge (U1) the billet to 65% of initial billet length

3) Anneal (A1) billet at 1370° C.

4) Forge-back billet to 197 mm diameter (FB1)

5) Upset forge (U2) billet to 65% of initial billet length

6) Forge-back billet to 197 mm diameter (FB2)

7) Upset forge (U3) billet to 65% of initial billet length

8) Anneal (A2) billet at 1065° C.

9) Forge-back the billet to 133 mm diameter (FB3). Clean the surface bymachining, thus reducing the billet diameter to 127 mm

10) Cut the billet to length, 63.5 mm

11) Anneal (A3) billet at 1065° C.

12) Roll to thickness. A 5-degree tilt angle was used. The thickness ofthe piece was reduced by approximately 5-10% in each pass. The piece wasrotated 45 degrees about a vertical axis after each pass. The piece wasturned over after every 4 passes. The final thickness of the piece afterrolling was 7.5 mm.

13) Anneal (A4) at 1010° C.

14) Flatten

15) Samples were taken from the centre of the plate, the mid-radius ofthe plate and the edge of the plate, and the texture determined by EBSD,using a 15 μm step in both horizontal and vertical directions. Theresults are presented here in FIGS. 6A, 6B, 6C, and 6D and Tables 6A and6B in the same way as for Example 1, except that the width examined was1.80 mm rather than 1.5 mm. The average grain size was about ASTM 6(approximately 40 μm ALI).

TABLE 6A 100 Grad 111 Grad 100 BF 111 BF Centre H1 −5.82 3.12 5.05 6.25Centre H2 5.62 −1.70 4.73 5.52 Mid-Rad H1 −6.92 −1.52 4.45 3.76 Mid-RadH2 6.85 1.17 5.97 5.87 Edge H1 −7.00 2.81 5.42 4.89 Edge H2 4.96 0.507.49 7.82

TABLE 6B Centre Mid-Rad Edge A/P Range H1-100 32 32 35  3 H1-111 22 2122  1 H2-100 27 38 30 11 H2-111 29 22 31  9

Example 7 (Inventive)

A plate 7.5 mm thick was made, using the same powder-metallurgy processas was described above, (steps 1 to 6), resulting in a puck 165 mmdiameter and 42 mm thick.

It was then rolled to thickness. A 5-degree tilt angle was used. Thethickness of the piece was reduced by approximately 5-10% in each pass.The piece was rotated 45 degrees about a vertical axis after each pass.The piece was turned over after every 4 passes. The final thickness ofthe piece after rolling was 7.5 mm. The finish-processing (annealingetc.) was performed conventionally.

Samples were taken from the centre of the plate, the mid-radius of theplate and the edge of the plate, and the texture determined by EBSD,using a 15 μm step in both horizontal and vertical directions. Theresults are presented here (FIGS. 7A, 7B, 7C and 7D) in the same way asfor Example 1, except that the width examined was 1.64 mm rather than1.5 mm, and the graph shows area percentage from 0% to 60% rather than0% to 70%. The average grain size was about ASTM 6½ (32 microns ALI).

TABLE 7A 100 Grad 111 Grad 100 BF 111 BF Centre H1 −1.78 2.10 3.46 3.21Centre H2 1.60 1.85 4.09 4.45 Mid-Rad H1 −1.11 1.20 3.94 3.77 Mid-Rad H22.84 2.70 4.46 4.82 Edge H1 −1.06 0.97 3.46 3.68 Edge H2 0.54 0.50 2.454.47

TABLE 7B Centre Mid-Rad Edge A/P Range H1-100 23 20 18 5 H1-111 27 29 282 H2-100 27 23 21 6 H2-111 29 28 27 2

Example 8 (Inventive)

Three plates about 8 mm thick were made using the ingot-metallurgyprocess described above, including the following process details:

1) Clean the surface of the ingot by machining. Cut the ingot (195 mmdiameter) to length, 374 mm, resulting in a weight of 474 lbs.

2) Upset forge (U1) the billet to 65% of initial billet length

3) Anneal (A1) billet at 1370 C

4) Forge-back billet to 197 mm diameter (FB1)

5) Upset forge (U2) billet to 65% of initial billet length

6) Forge-back billet to 197 mm diameter (FB2)

7) Anneal (A2) billet at 1065 C

8) Upset forge (U3) billet to 65% of initial billet length

9) Forge-back the billet to 133 mm diameter (FB3). Clean the surface bymachining, thus reducing the billet diameter to 127 mm

10) Cut the billet to length, 68.6 mm

11) Upset forge (U4) billet to 50.8 mm

11) Anneal (A3) billet at 1065 C

12) Roll to 25.4 mm thickness using conventional (straight) rolling. Thethickness of the piece was reduced by approximately 20% in each pass.The piece was rotated 90 degrees about a vertical axis after each pass.

13) Roll to final thickness. A 5-degree tilt angle was used. Thethickness of the piece was reduced by approximately 10% in each pass.The piece was rotated 45 degrees about a vertical axis after each pass.The piece was turned over after every pass. The final thickness of thepiece after rolling was 8 mm

14) Anneal (A4) at 955 C

15) Flatten.

In the case of 1 plate, samples were taken from the centre of the plate,the mid-radius of the plate and the edge of the plate (2 samples, wellseparated), and the texture determined by EBSD, using a 15 μm step inboth horizontal and vertical directions. The results are presented inFIGS. 8A, 8B, 8C, 8D and 8E, and in Tables 8A and 8B, in the same way asfor Example 1. In the case of the other 2 plates, only edge samples (2samples, well separated) were taken. The average grain size was aboutASTM 7½ (24 microns ALI).

TABLE 8A Plate 1 100 Grad 111 Grad 100 BF 111 BF Centre H1 −1.40 −0.633.97 4.31 Centre H2 2.12 −3.04 5.12 4.51 Mid-Rad H1 −3.18 1.58 4.09 4.85Mid-Rad H2 2.14 −4.04 3.55 4.47 Edge 1 H1 −5.33 1.96 4.62 5.23 Edge 1 H2−1.50 −0.73 4.17 5.31 Edge 2 H1 −4.35 0.46 3.55 6.33 Edge 2 H2 4.66−1.68 4.35 4.73 Plate 2 Edge 1 H1 −5.30 4.78 5.51 3.68 Edge 1 H2 1.25−0.59 4.46 4.33 Edge 2 HI −1.74 −0.46 5.78 4.79 Edge 2 H2 −0.88 2.655.87 5.26 Plate Edge 1 H1 −7.56 1.57 4.74 4.50 Edge 1 H2 4.08 −2.21 3.914.68 Edge 2 H1 0.07 2.35 5.33 5.43 Edge 2 H2 −0.71 −4.67 6.62 5.33

TABLE 8B Plate 1 Centre Mid-Rad Edge 1 Edge 2 A/P Range H1-100 30.3 28.526.6 26.6 3.7 H1-111 30.5 25.9 29.3 27.6 4.6 H2-100 28.3 25.0 21.7 23.96.6 H2-111 32.7 30.5 31.1 28.5 4.2

Summary

The examples of the invention can be conveniently compared to the fourexamples of the old art in the following summary table. To calculate theaverage gradient, the absolute value of each individual gradient valueis used. The Max. Grad. shown is the maximum found in any of the samplestaken, which in the case of all the inventive examples, includes edge,mid-radius and centre locations. The lower each value is, the moreuniform the texture of the plate.

TABLE 9 Ave Max Ave Max Ave A/P Max A/P Grad Grad BF BF Range RangeExample 1 6.4 14.4  7.3 9.2 13.2  22    Example 2 8.1 13.3  6.0 7.9 6.48.1 Example 3 5.6 9.0 5.3 7.9 4.7 7.6 Example 4 6.8 15.1  4.7 7.7 N/AN/A Example 5 2.9 8.5 6.0 7.8 3.7 7   Example 6 4.0 7.0 5.6 7.8 6.011    Example 7 1.5 2.8 3.9 4.5 3.7 6   Example 8 2.5 7.6 4.9 6.6 4.86.6 N/A means “Not Available”.

It can be seen from Table 9 (in which Examples 3 and 7 use powdermetallurgy, and the others use ingot metallurgy) that:

1) All the comparative examples have average gradients above 5% per mm.

2) Of the comparative examples, Example 3 (powder metallurgy method) hasmore uniform texture than Examples 1, 2 and 3 (ingot metallurgy).

3) All the inventive examples have average gradients below 5% per mm,and some examples of both powder metallurgy and ingot metallurgy haveaverage gradients less than half those of the relevant comparativeexamples.

4) Of the inventive examples, Example 7 (powder metallurgy) has moreuniform texture than Examples 5, 6 and 8 (ingot metallurgy).

5) The banding factors and A/P ranges in some inventive examples are notjust equivalent to, but are actually lower than, the relevantcomparative examples.

Also, it is instructive to compare Examples 3, 4 and 8, because themultiplicity of plates in each of these examples allows statisticalanalysis and thus comparison of variability of texture from plate toplate. The edge samples (19 samples from Example 4, 6 samples from eachof the other examples) are compared in Table 10.

TABLE 10 100% 111% l00 Grad 111 Grad 100 Biz 111 BF Ex. 4 Average 19.3 32.0  5.4 8.7 4.7 7.5 Ex. 4 Std. Dev. 3.9 5.3  1.60  2.78  1.42  1.82 Ex.3 Average 24.3  30.5  6.1 6.0 4.4 5.7 Ex. 3 Std. Dev.  2.15  1.99  1.47 2.04  0.53  0.88 Ex. 8 Average 27.7  27.2  3.1 2.0 4.9 5.0 Ex. 8 Std.Dev.  3.80  2.11  2.38  1.48  0.91  0.67

Although standard deviations from 12 data-points are not very accurate,it can be seen that the variability in Example 8 (as shown by theStandard Deviations of Table 10) is similar to that in Examples 3 and 4.The lower average gradients of Example 8, compared to Examples 3 and 4,are high-lighted in the table.

Whereas particular embodiments of this invention have been describedabove for purposes of illustration, it will be evident to those skilledin the art that numerous variations of the details of the presentinvention may be made without departing from the invention as defined inthe appended claims.

1.-38. (canceled)
 39. A method of forming a refractory metal plate, themethod comprising: (A) providing a workpiece having a size suitable fora target plate, the workpiece comprising a refractory metal; (B)asymmetrically rolling the workpiece one or more times at an angle ofincline between 2° and 20° relative to horizontal, thereby forming arolled plate; and (C) annealing the rolled plate to achievesubstantially full recrystallization.
 40. The method of claim 39,wherein providing the workpiece comprises separating the workpiece froman ingot.
 41. The method of claim 40, wherein the ingot is anelectron-beam-melted ingot.
 42. The method of claim 39, whereinproviding the workpiece comprises separating the workpiece from apowder-metallurgy billet.
 43. The method of claim 42, further comprisingproviding the powder-metallurgy billet by a process comprising: (a) coldisostatically pressing a refractory metal powder to a density of 60%-90%to form a preform; (b) hot isostatically pressing the preform to adensity of approximately 100% to form a billet; and (c) annealing thebillet.
 44. The method of claim 39, wherein the angle of incline isbetween 3° and 7°.
 45. The method of claim 39, wherein the workpiece isasymmetrically rolled a plurality of times during step (B).
 46. Themethod of claim 45, wherein the workpiece is rotated at a predeterminedangle about a vertical axis between rolling passes.
 47. The method ofclaim 45, wherein the workpiece is flipped between rolling passes. 48.The method of claim 39, further comprising, after step (C), bonding theplate to a backing plate.
 50. The method of claim 39, wherein, afterstep (C): the plate has a crystallographic texture as characterized bythrough thickness gradient, banding severity, and variation across theplate for at least one of the texture components 100//ND or 111//ND,using electron back-scatter diffraction with a 15 μm step in both thehorizontal and vertical directions for each measurement; an averagethrough-thickness gradient is less than or equal to 6% per mm for111//ND; and a maximum through-thickness gradient is less than or equalto 13% per mm for 111//ND.
 51. The method of claim 39, wherein, afterstep (C): the plate has a crystallographic texture as characterized bythrough thickness gradient, banding severity, and variation across theplate for at least one of the texture components 100//ND or 111//ND,using electron back-scatter diffraction with a 15 μm step in both thehorizontal and vertical directions for each measurement; and an averagebanding severity is less than or equal to 6% per mm for 111//ND.
 52. Themethod of claim 39, wherein, after step (C): the plate has acrystallographic texture as characterized by through thickness gradient,banding severity, and variation across the plate for at least one of thetexture components 100//ND or 111//ND, using electron back-scatterdiffraction with a 15 μm step in both the horizontal and verticaldirections for each measurement; and a maximum banding severity is lessthan or equal to 8% per mm for 111//ND.
 53. The method of claim 39,further comprising, after step (C): providing a substrate; andsputtering the plate to form a film on the substrate, the filmcomprising the refractory metal.
 54. The method of claim 39, wherein therefractory metal comprises tantalum.
 55. The method of claim 39, furthercomprising annealing the workpiece before step (B).
 56. The method ofclaim 39, further comprising applying a lubricant to top and bottomsurfaces of the workpiece before asymmetrically rolling the workpiece.